Genetic Variability for Tuber Yield, Quality, and Virus Disease Complex Traits in Uganda Sweetpotato Germplasm

Sweetpotato (Ipomoea batatas) is an important root crop in Uganda, where yield potential and quality attributes have not been fully exploited due to limited breeding efforts and poor knowledge on the inheritance of some of its agronomic traits. A study was carried out at Makerere University to phenotypically characterise selected sweetpotato cultivars with special reference to sweet potato virus disease (SPVD) resistance, growth habit, flowering and seed set ability, tuber yield and shape, tuber skin and flesh colour, dry matter, starch, sugar and βcarotene content. Twenty cultivars were selected for use in the assessment of their breeding potential and for improvement of yield and quality attributes. Cultivar Munyeera displayed the highest level of SPVD resistance followed by New Kawogo and Polyster as exhibited by relative area under disease progress curves following natural field infection and graft inoculation with SPVD causing viruses, Sweet potato chlorotic stunt virus and Sweet potato feathery mottle virus. Flowering ability was low in some cultivars and a few did not flower at all. Some cultivars e.g. Munyeera, New Kawogo, Silk and Sowola which showed high flowering ability failed to fertilise and set seed when crossed to specific cultivars. Preliminary genetic analysis for yield and quality following crossing elite 7 female and 6 male cultivars in a North Carolina 2 mating design showed wide genetic variability in the F1s for the important traits, and heterosis was observed for some traits such as tuber size and number of tubers per plant. Up to five genes may be involved in β-carotene synthesis and probably in combination with other genes in different genetic backgrounds that can modify flesh colour from white to purple. The results demonstrate the possibility to improve sweetpotato for yield and quality using the available germplasm.